The use of hot melt adhesives as substitutes, or even replacements, for conventional solvent-based adhesives in various applications has been increasingly favored because of environmental concerns caused by the emission of volatile organic compounds (VOCs), the well-being of workers in the workplace, and faster setting times than solvent-based adhesives.
A variety of hot melt adhesive formulations, polymeric modifiers and other applications include an amorphous polyalphaolefin (APAO). In such formulations, it is important that the polymer exhibit such characteristics as a range of tightly controlled BROOKFIELD.RTM. melt viscosities (MVs), needle penetrations (NPs) and ring & ball softening points (RBSPs, or R & B SPs), controllable and predictable long open time (OTs), low temperature flexibility, adhesion to a variety of substrates and compatibility with a variety of tackifiers and waxes. It is desirable to use such raw materials with reproducible specifications to obtain consistent properties in the formulations used in adhesive and other formulations.
It is well known that crystalline polypropylene generally has an isotactic or syndiotactic structure, and that amorphous polymers, such as atactic polypropylene, generally have a considerable atactic structure having low crystallinity. U.S. Pat. Nos. 3,112,300 and 3,112,301, for example, describe isotactic polypropylene and provide structural formulae for isotactic and syndiotactic polypropylene polymers. The former is a straight chain of propylene units wherein the methyl groups are all aligned on one side of the polymer chain. In the latter, the methyl groups alternate from one side of the chain to the other. Atactic polypropylenes, on the other hand, have methyl chains randomly disposed on opposite sides of the polymer chain. In the isotactic and syndiotactic polypropylenes of the patents above, the regularity of structure tends to result in a more highly crystalline material. Atactic polypropylene polymers of low molecular weight typically result in gummy materials having minimal tensile strength. The isotactic or syndiotactic polymers have a variety of disadvantages, such as low elongation capabilities and no open time, due to their high crystallinity, making them undesirable in hot melt adhesive formulations.
Most of the polypropylene which is produced commercially is crystalline isotactic polypropylene. Conventional polymers of this type typically have a crystallinity, or heat of fusion, of 70 J/g or higher, and more typically 90 J/g or higher. These polymers are well known and have been the subject of many patents and articles.
APAO polypropylenes, which have very little strength, are used commercially in adhesives and as asphalt additives, for example. Conventional atactic polypropylenes that tend to have a crystallinity of less than 20 J/g typically have an extremely high melt flow rate of around 2,000 g/10 min. or higher (at 230.degree. C.). Generally, these atactic polypropylene polyolefins are sticky, which limits their possible usage in commercial products. Conventional LMW APAOs have not found much use in certain applications where high tensile and elongation values are required, because these APAOs lack such characteristics.
High-molecular weight ("HMW") APAOs, also called flexible polyolefin polymers or FPO polymers herein, such as amorphous propylene homo- and co-polymers, are important for their use in diverse products. The broad utility of these materials is due in large part to the unique combination of chemical and physical properties, such as chemical inertness, softness, flexibility, etc., exhibited by these materials. Conventional amorphous, or atactic, polypropylene is different from crystalline polypropylenes in steric microstructure, and usually lacks tensile strength, for example. It is also known that the combination of different polymers to obtain polymer blends for particular uses, however, makes conventional blends that tend to have several disadvantages, such as low melt viscosities, immiscibility that imparts optical haziness and two independent melting points (mp) and/or glass transition temperatures (T.sub.g), and poor or no open time.
Various references disclose some conventional polymer blends, some of which are discussed below. As used herein, the word "blend" or "blends" includes the mechanical polyblends, mechanochemical polyblends, chemical polyblends, solution-cast polyblends and latex polyblends described in the Kirk-Othmer Concise Encyclopedia of Chemical Technology, Volume 24, 3.sup.rd ed. Pp 920-922 (Wiley & Sons, N.Y., ISBN 0-471-86977-5), the entry for which is expressly incorporated herein by reference thereto. The word "blend" also includes physical mixtures of at least two polymeric materials.
U.S. Pat. No. 3,963,659 discloses homogeneous thermoplastic bituminous compositions containing up to 25 parts by weight of cross-linkable ethylene-.alpha.-olefin rubber, and methods for preparing the sane, to provide improved properties for use in asphalt applications. The cross-linkable rubbers in the bituminous compositions yield high tensile strength final products.
U.S. Pat. No. 4,022,728 discloses hot melt pressure sensitive adhesives made of blends of amorphous polyolefin, a LMW substantially amorphous polymer, a liquid tackifying resin, and crystalline polypropylene to provide good adhesive properties at low temperatures.
U.S. Pat. No. 4,075,290 discloses polymer blends having a major amount of isotactic polybutene-1 having a molecular weight of 500,000 to 1,750,000 with a minor amount of low-pressure ethylene with a polypropylene or butene-1 copolymer having a molecular weight of 200,000 to 350,000, where the blends allegedly exhibit excellent weldability and superior tear and rupture resistance.
U.S. Pat. No. 4,650,830 discloses a thermoplastic elastomer composition allegedly having good injection fusion bondability and surface gloss properties made of an amorphous ethylene/.alpha.-olefin copolymer and (i) a low crystallinity copolymer of propylene with an .alpha.-olefin having at least 4 carbon atoms, (ii) a polymer composed mainly of 1-butene, or (iii) a combination of the low crystallinity copolymer or the mainly 1-butene polymer with a high crystallinity polymer made mostly of propylene and at least some of the components are crosslinked.
U.S. Pat. No. 4,960,820 discloses a blend of less than about 10 weight percent LMW, isotactic poly-1-butene polymer having a melt index of greater than 100 to 1000, and at least about 90 weight percent of a propylene polymer having a melt index of less than 60.
U.S. Pat. No. 5,468,807 discloses a resin composition including 20-80 weight percent of an amorphous polyolefin having a propylene and/or butene-1 component of at least 50 weight percent, and 20-80 weight percent of a crystalline polypropylene, which is allegedly well-balanced in mechanical strength and flexibility.
U.S. Pat. No. 5,478,891 discloses blended polymer compositions of (a) a HMW copolymer of ethylene and an alphaolefin having at least 4 carbons, and (b) an amorphous polypropylene and/or amorphous polyolefin, or mixtures thereof, for use in hot melt adhesives, coatings, sealants, asphalt or bitumen modifiers, and plastics additives. Component (a) is described as generally rigid at room temperatures and component (b) is described as having a molecular weight range of about 300 to 60,000, where the blends have a viscosity of between approximately 650 to 46,000 cPs.
U.S. Pat. No. 5,512,625 discloses a thermoplastic hot-melt adhesive from a polymer blend of (a) an oligomer of an alpha-olefin having at least eight carbon atoms in the monomer and an oligomer molecular weight of less than 5,000, and (b) a mixture of a substantially amorphous poly-alpha-olefin and a substantially crystalline poly-alpha-olefin to provide an allegedly improved impact strength, viscosity of between about 130 to 18,000 cPs from 180.degree. C. to 200.degree. C., and flexibility at low temperatures.
It has also been known to use certain types of polymers and polymer blends in fibers for use in non-woven applications, such as webs, films, foams, and the like. For example, EP Publication No. 0,586,937 A1 discloses a non-woven fabric made with multi-component polymeric strands including a blend of polyolefin and elastomeric thermoplastic material in one side or as the sheath of multi-component polymeric strands.
U.S. Pat. No. 5,719,219 discloses a melt extrudable, moisture curable thermoplastic polymer produced from a silane modified elastomeric polymer.
U.S. Pat. No. 5,714,256 discloses methods for producing non-woven fabrics with a wider bonding window by forming the webs from thermoplastic polymer blends having 0.5 weight percent to 25 weight percent syndiotactic polypropylene. Such webs may then be thermally bonded to the non-woven web, and have a bonding window at least 10.degree. F. wider than that of a similar web without syndiotactic polypropylene.
It would be advantageous, however, to produce polyolefin blends having improved properties, such as processing characteristics and durability, for use in non-woven products. It is also desired to produce a polymer blend for use in a non-woven product, wherein the blend has a sufficiently high melt viscosity to provide tensile strength, yet has a low crystallinity and a high elongation capability. It is also desired to obtain polymer blends that have a sufficiently high "open time" to impart adhesive characteristics. It is also desired to produce a polymer blend for use in adhesives using two miscible polymers having similar crystallinities, such that the resulting polymer blend has substantial transparency and a single T.sub.g and melting point, for example. These characteristics are desired in polymer blends to create polymers having a variety of new uses and improved capabilities, including non-woven products and adhesives.